1. Field of the Invention
This invention relates to gel formulations that are blood compatible and shear sensitive. More particularly, such gel formulations comprising a polydimethylsiloxane-polyethyleneoxide copolymer gelled with dibenzylidine sorbitol in the presence of water or alcohol, are particularly useful for facilitating the separation of blood serum or plasma from the cellular portion of blood or as a thermoreversible shear-sensitive substance for use in mechanical serum separation devices.
2. Description of Related Art
Biochemical tests carried out in a clinical laboratory require use of blood serum or plasma as a sample. For preparing the sample for examination, it is frequently necessary to separate the blood serum or plasma from the solid blood components. There are known various types of blood separating compositions which are used to separate the blood components from one another.
Some blood separating compositions are formulated into thixotropic gels. For example, fumed silica to crosslink polar polyester or fatty oils into a gel or fumed silica to form a reversibly-formed network of silica particles to gel nonpolar oils.
U.S. Pat. Nos. 3,852,194, 3,920,549 and 3,997,442 disclose dibenzylidene sorbitol (DBS) gels of hydrocarbon or silicone oils that have an opaque characteristic. DBS is a gelling agent that is capable of forming a molecular network. Unlike the thixotropic gels, DBS gels of hydrocarbon or silicone oils loose all structural integrity under stress, liquefy under centrifugation, and do not reform into a solid gel. Consequently, these gels are not adequate for separating blood into liquid and solid components.
Furthermore, use of hydrophobic hydrocarbon or silicone oils in blood collection tubes is problematic. As disclosed in U.S. Pat. No. 5,257,633, blood components such as cells and fibrin clots adhere tenaciously to non-water wettable surfaces. Therefore, when the inside walls of blood collection tubes become coated with the hydrocarbon or silicone type oils of these gels, cells and clot debris will adhere, preventing clean separation of liquid and solid components of blood. Therefore, hydrocarbon and silicone type oils are not blood compatible in blood collection applications.
Whereas there are numerous publications related to gelled silicones, hydrocarbons, and polyesters there are no publications that suggest or teach that polymers containing polar ethyleneoxide moieties can be gelled with dibenzylidine sorbitol (DBS) in the presence of polar liquids yielding gels that will flow under shear forces involved in centrifugation, will not liquefy under shear, are readily gelled using water or alcohol and are compatible in blood collection applicatons.